DFX - MXT Question

[Ralph Bryant]

Is the ground-phase readout of both the DFX and MXT calibrated the same on both machines ? Do both give the same reading in one particular location ? I'm assuming they are both operating at higher kHz and are not normalized on the DFX. Is this correct ?

Thanks,

Ralph

 

[Jeff Foster]

The DFX uses the VDI scale to report ground phase via the DC Phase feature. The MXT reports the ground phase via its unique GND scale. Both machines use very similar frequencies for this purpose (MXT: 14kHz, and DFX: 15kHz). The conversion between the two scales is non-linear, however the boundary conditions are as follows: -95 VDI ~= 84 GND and +6 VDI ~= 3 GND. The GND scale provides much more precision in the near ferrous region, with the VDI range of -95 to -88 corresponding approximately to the GND range of 84 to 50.

Hope this helps.

Jeff

<font color="#00C000">Have a happy Holiday Season.</font>

 

[CWRelichunter]

[Just to throw a curve on the DFX DC Phase readings]

When I owned my DFX the hottest ground I hunted in read -97.4 on DC Phase.

I therefore do not believe that the DC Phase of the DFX (or XLT) is based on the exact same VDI scale of -95 to 95.

Maybe I had a defective DFX, maybe not. But it was my impression that the DC phase max potential was two digits to the left of the decimal point, and one to the right. Meaning, -99.9 is possible (if anything could register that hot.)

J in VA

 

[Ralph Bryant]

Thanks Jeff, that does help answer my question, but then raises another.

I notice that the VDI scale of the ground phase on the DFX is broken down into readings of tenths (1/10) decimal compared to whole numbers of the MXT GND scale. It would appear that the DFX scale actually provides the better, more consistent and linear scale resolution of the two, since there would effectively be 1010 possibilities on the DFX VDI scale compared to the 81 possibilities of the MXT scale between their respective boundaries. Am I assuming correctly ?

Also, the GND scale of the MXT appears to be more arbitrary and confusing than the VDI scale of the DFX to me personally.

Thanks again for the info. Just bouncing these two machines back and forth as to possibilities for a new purchase. Also enjoying your "Digging Deeper".....excellent information !

Ralph

 

[Jeff Foster]

It is my understanding, from working with White's engineering, that the DFX is factory calibrated for VDI -95 as the boundary for the most ferrous ground and the MXT is factory calibrated for GND 84 to be the boundary for the most ferrous ground.

However, on the MXT, to quote its design engineer, David Johnson, "In a perfect world, with ferrite balancing at 84, nothing would ever fall higher. However, with drift, noise, and/or the presence of ground discontinuities or targets, higher numbers can occur."

Similar factors are also at play on the DFX.

Enjoy.

<font color="#00C000">Have a happy Holiday Season.</font>

 

[Jeff Foster]

<b>"It would appear that the DFX scale actually provides the better, more consistent and linear scale resolution of the two, since there would effectively be 1010 possibilities on the DFX VDI scale compared to the 81 possibilities of the MXT scale between their respective boundaries. Am I assuming correctly ?</b>

Merely tacking digits on to the right of the decimal point doesn't necessarily make for better precision if the underlying mechanism doesn't support less error. On the MXT, there is a difference in the basic design that enhances phase resolution in the extreme negative (and positive, since the VDI scale is like a wheel with -95 back to back with +95) regions of the scale. This implicit feature in the MXT allows the GND scale to be more precise than the VDI scale near -95 (GND 84).

In addition, a common difficulty with when using higher frequencies (~14kHz vs 6.6kHz) for coin hunting is that the raw VDI response (phase shift) of conductive targets tend to "bunch up" at the high end of the scale, making target ID more difficult. The same implicit design feature that improves the GND number precision for ferrous ground also helps improve conductive target ID'ing. (It also helps to lessen the sensitivity reducing effects of the ground-balance from wrapping around from the -95 end of the VDI scale to the +95 end.)

<b>"Also, the GND scale of the MXT appears to be more arbitrary and confusing than the VDI scale of the DFX to me personally."</b>

I agree.

<b>Also enjoying your "Digging Deeper".....excellent information !</b>

Thanks. I'm glad you're finding the book helpful.

Enjoy.

<font color="#00C000">Have a happy Holiday Season.</font>